Pressure sensors with tensioned membranes

ABSTRACT

Pressure sensors having ring-tensioned membranes are disclosed. A tensioning ring is bonded to a membrane in a manner that results in the tensioning ring applying a tensile force to the membrane, flattening the membrane and reducing or eliminating defects that may have occurred during production. The membrane is bonded to the sensor housing at a point outside the tensioning ring, preventing the process of bonding the membrane to the housing from introducing defects into the tensioned portion of the membrane. A dielectric may be introduced into the gap between the membrane and the counter electrode in a capacitive pressure sensor, resulting in an improved dynamic range.

CROSS-REFERENCE TO RELATED APPLICATION(S)

The application is a divisional of U.S. application Ser. No. 15/485,190filed on Apr. 11, 2017, which claims priority to and the benefit of U.S.Provisional Application Nos. 62/320,897 and 62/320,889, both filed Apr.11, 2016, entitled “CAPACITIVE PRESSURE SENSORS WITH RING STABILIZINGMEMBRANES”, the entire content of which is incorporated herein byreference in its entirety.

BACKGROUND

The following Background discussion is only for enhancement ofunderstanding of the background of the invention, and therefore it maycontain information that does not form the prior art that is alreadyknown to a person of ordinary skill in the art.

Some pressure sensors utilize membranes to measure the pressure on themembrane, often relative to a reference pressure inside the pressuresensor. The sensor measures the deflection of the membrane to determinewhat the pressure differential being experienced by the pressure sensoris. The characteristics of the membrane play a role in determining themagnitude of that deflection. In precision sensors, defects in amembrane such as defects introduced in the process of producing themembrane or defects introduced in the process of fabricating thepressure sensor can prevent a sensor from making accurate readings.Additionally, some pressure sensors require high sensitivity over alarge dynamic range, and some pressure sensors such as implantablepressure sensors require a small profile. These two considerations maybe at odds. There is an ongoing need for more accurate, more reliable,smaller, and easier to fabricate pressure sensors.

SUMMARY

According to aspects of embodiments of the present disclosure, pressuresensors having ring-tensioned membranes, pressure sensors havingplate-tensioned membranes, pressure sensors having improved dynamicranges, and methods of making the same are disclosed.

In one aspect of the present disclosure, a pressure sensor is provided.The pressure sensor includes a housing having an opening, a membranecoupled to the housing at the opening, a tensioning ring coupled to themembrane configured to apply a tensile force to the membrane, and asensor circuit in the housing configured to generate a pressure signalbased on a deflection of the membrane.

In one embodiment, the membrane has a first coefficient of thermalexpansion, the tensioning ring has a second coefficient of thermalexpansion lower than the first coefficient of thermal expansion, and themembrane and the tensioning ring are configured to be bonded togetherwhen heated to above an operating temperature range while the membraneexperiences greater expansion than the tensioning ring and thetensioning ring applies the tensile force to the membrane at theoperating temperature range.

In one embodiment, the membrane has a tensioned region and anon-tensioned region, the tensioned region of the membrane is an area ofthe membrane inside the tensioning ring, the non-tensioned region of themembrane is an area of the membrane outside the tensioning ring, and thenon-tensioned region of the membrane is bonded to the housing.

In one embodiment, the pressure sensor includes a counter electrode, aspacer, and an isolator, wherein the membrane comprises an electrode,the counter electrode is positioned parallel to the membrane, the spaceris positioned between the counter electrode and the membrane to providea gap between the counter electrode and the membrane, the tensioningring comprises a retaining portion, the retaining portion of thetensioning ring is configured to hold the counter electrode against thespacer, the isolator is configured to isolate the counter electrode fromthe tensioning ring, and the sensor circuit is configured to evaluate acapacitance between the electrode and the counter electrode.

In one embodiment, the isolator includes the spacer.

In one embodiment, the isolator includes a dielectric between thecounter electrode and the membrane, the spacer having a first thicknessbetween the counter electrode and the membrane, and the dielectrichaving a second thickness less than the first thickness.

In one embodiment, the membrane is a thin sheet of metal.

In one embodiment, the membrane comprises titanium, stainless steel, oran alloy.

In another aspect of the present disclosure, a pressure sensor isprovided. The pressure sensor includes a housing having an opening, amembrane coupled to the housing at the opening, a tensioning platepositioned parallel to the membrane with a gap between the tensioningplate and the membrane, a bonding ring coupled to the membrane and thetensioning plate, wherein the tensioning plate is configured to apply atensile force to the membrane through the bonding ring, and a sensorcircuit in the housing configured to generate a pressure signal based ona deflection of the membrane.

In one embodiment, the bonding ring is an electrical insulator, themembrane comprises an electrode, the tensioning plate comprises acounter electrode, and the sensor circuit is configured to evaluate acapacitance between the electrode and the counter electrode.

In one embodiment, the bonding ring comprises an adhesive and aplurality of spherical spacers, each of the plurality of sphericalspacers having a single diameter, and each of the plurality of sphericalspacers being an electrical insulator.

In another aspect of the present disclosure, a method of fabricating apressure sensor is provided. The method includes heating a membranehaving a first coefficient of thermal expansion and a tensioning ringhaving a second coefficient of thermal expansion lower than the firstcoefficient of thermal expansion to a temperature outside an operatingtemperature range of the pressure sensor, bonding the tensioning ring tothe membrane at the temperature outside the operating temperature rangeof the pressure sensor while the membrane experiences greater expansionthan the tensioning ring, and fixing the membrane and the tensioningring to a sensor housing comprising a sensor circuit while the membraneand the sensor housing are at about the same temperature.

In one embodiment, the fixing of the membrane and the tensioning ring tothe sensor housing is bonding the sensor housing to an area of themembrane outside the area bonded to the tensioning ring.

In another aspect of the present disclosure, a method of fabricating apressure sensor is provided. The method includes heating a membranehaving a first coefficient of thermal expansion and a tensioning platehaving a second coefficient of thermal expansion lower than the firstcoefficient of thermal expansion to a temperature outside an operatingtemperature range of the pressure sensor, bonding the tensioning plateto the membrane with a bonding ring at the temperature outside theoperating temperature range of the pressure sensor while the membraneexperiences greater expansion than the tensioning plate, and fixing themembrane and the tensioning plate to a sensor housing comprising asensor circuit while the membrane and the sensor housing are at aboutthe same temperature.

In one embodiment, the fixing of the membrane and the tensioning plateto the sensor housing comprises bonding the sensor housing to an area ofthe membrane outside the area bonded to the tensioning plate by thebonding ring.

In another aspect of the present disclosure, a pressure sensor isprovided. The pressure sensor includes a membrane, the membranecomprising an electrode, a counter electrode positioned parallel to themembrane, a spacer between the membrane and the counter electrode, thespacer having a first thickness between the membrane and the counterelectrode, a dielectric between the membrane and the counter electrode,the dielectric having a second thickness less than the first thicknessof the spacer, and a sensor circuit configured to evaluate a capacitancebetween the electrode and the counter electrode.

In one embodiment, the membrane is configured to not be in contact withthe dielectric when under pressures in a first pressure range, and themembrane is configured to be in contact with the dielectric when underpressures in a second pressure range.

In one embodiment, the sensor circuit is configured to measure thecapacitance over the first pressure range and the second pressure range.

In one embodiment, the pressure sensor has a first dynamic range whenthe membrane does not contact the dielectric, and a second dynamic rangewhen the membrane does contact the dielectric.

In one embodiment, the membrane is configured to come in contact withthe dielectric at pressures within an operating pressure range of thepressure sensor.

In one embodiment, the membrane is configured to contact the dielectricand wherein the sensor circuit generates a pressure signal based on anamount of a surface area of the membrane in contact with the dielectric.

In one embodiment, the pressure sensor includes a tensioning ring toapply a tensile force to the membrane.

These and other features and aspects of the present invention will bemore fully understood when considered with respect to the followingdetailed description, appended claims, and accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, together with the specification, illustratepreferred and example embodiments of the present invention, and,together with the description, serve to explain the principles of thepresent invention.

FIG. 1 is a ring-tensioned membrane according to embodiments of thepresent disclosure.

FIG. 2 is a cross sectional perspective view of an embodiment of apressure sensor utilizing a ring-tensioned membrane according toembodiments of the present disclosure.

FIG. 3A is a plate-tensioned membrane according to embodiments of thepresent disclosure.

FIG. 3B is a cross sectional perspective view of the plate-tensionedmembrane of FIG. 3A.

FIG. 4 is a cross sectional perspective view of an embodiment of apressure sensor utilizing a plate-tensioned membrane according toembodiments of the present disclosure.

FIG. 5 is a cross sectional perspective view of an embodiment of apressure sensor according to embodiments of the present disclosure.

FIG. 6A is an exploded view of a ring-tensioned membrane for acapacitive sensor according to embodiments of the present disclosure.

FIG. 6B is a cross section view of the ring-tensioned membrane of FIG.6A.

FIG. 7A is an exploded view of a ring-tensioned membrane for acapacitive sensor according to embodiments of the present disclosure.

FIG. 7B is a cross section view of a ring-tensioned membrane for acapacitive sensor according to embodiments of the present disclosure.

FIG. 8A is an assembly for a capacitor for a capacitive pressure sensorhaving an increased dynamic range according to embodiments of thepresent disclosure.

FIG. 8B is a first subassembly of the capacitive sensor of FIG. 8A.

FIG. 8C is a second subassembly of the capacitive sensor of FIG. 8A.

FIG. 8D is a cross section view of the assembly for the capacitivesensor of FIG. 8A.

FIG. 9 is a cross sectional perspective view of an embodiment of acapacitive pressure sensor utilizing a capacitor according toembodiments of the present disclosure.

FIG. 10 is a graph depicting the capacitance and sensitivity at givenpressures of a capacitive pressure sensor according to embodiments ofthe present disclosure.

DETAILED DESCRIPTION

In the following detailed description, only certain example embodimentsof the present invention are shown and described, by way ofillustration. As those skilled in the art would recognize, the inventionmay be embodied in many different forms and should not be construed asbeing limited to the embodiments set forth herein. Descriptions offeatures or aspects within each example embodiment should typically beconsidered as available for other similar features or aspects in otherexample embodiments. Like reference numerals designate like elementsthroughout the specification.

FIG. 1 is a ring-tensioned membrane according to embodiments of thepresent disclosure. The membrane 110 may be used in a pressure sensorwhich measures the deflection of the membrane 110 to detect thedifference in pressure applied to opposite faces of the membrane 110. Insome embodiments, for example where the membrane is used in animplantable pressure sensor, the membrane may be made of a biocompatiblematerial such as titanium, a titanium alloy, and/or stainless steel.

A tensioning ring 120 is coupled to the membrane 110. The tensioningring 120 has an outer (e.g. circumferential) region which may directlyor indirectly contact the membrane surrounding an inner region whichdoes not contact the membrane 110. The tensioning ring 120 may be madeof a metal, for example molybdenum, a metal alloy, for example Kovar orInvar, and/or another material, for example fused silica, silicon,glass, or a ceramic. The tensioning ring 120 may be bonded to themembrane 110. For example, in some embodiments, the tensioning ring 120is welded or soldered to the membrane 110. In other embodiments, theyare bonded together using an adhesive such as an epoxy.

The tensioning ring 120 applies a tensile force to the portion of themembrane 110 inside the area bonded to the tensioning ring 120(hereinafter ‘the inner portion of the membrane’) (e.g. the tensionedregion). This tensile force may pull the membrane flat, reducing oreliminating warping of the membrane 110 which may have occurred duringthe production process. The tensioning ring 120 may apply the tensileforce to the membrane 110 because the membrane 110 contracts relative tothe tensioning ring 120 after they are bonded together. In someembodiments, the tensioning ring 120 has a lower coefficient of thermalexpansion (CTE) than the membrane 110. The pressure sensor has anoperating temperature range, referring to the temperatures which thepressure sensor may be expected to be exposed to during typicaloperation. This operating temperature range may vary based on theintended application of the pressure sensor. For example, where thepressure sensor is an implantable pressure sensor, the operatingtemperature range may be the temperatures expected to be experiencedwithin the human body. Both the tensioning ring 120 and the membrane 110are heated to a temperature above the anticipated operating temperatureof the pressure sensor when they are bonded together, and both willcontract when reduced to temperatures in the operating temperaturerange. The membrane 110 will contract more than the tensioning ring 120based on its lower CTE, resulting in the tensioning force.Alternatively, in another embodiment, the membrane 110 is heated at thetime of bonding, resulting in expansion, but the tensioning ring 120 isnot heated or is heated to a lesser degree. The tensioning ring 120 mayhave a greater stiffness than the membrane 110 (e.g. a greater relativestiffness) which causes the membrane 110, not the ring 120, to bedeformed by the tensile force.

FIG. 2 is an embodiment of a pressure sensor utilizing thering-tensioned membrane of FIG. 1 . The membrane 210, tensioned by thetensioning ring 220, is coupled to a housing 242, defining ahermetically sealed cavity inside the housing 242. The housing 242 maybe bonded to the membrane 210 at an area 230 outside the area bonded tothe tensioning ring 220 (hereinafter ‘the outer portion of themembrane’) (e.g., the non-tensioned region). In some embodiments, thisbond is made through laser welding. The tensioning ring 220 may isolatethe inner portion of the membrane 210 from any warping or other defectsintroduced during the process of bonding the housing 242 to the outerportion of the membrane 210. In some embodiments, the membrane 210 andthe housing 242 are at approximately the same temperature when bondedtogether, and/or the membrane 210 and the housing 242 have approximatelythe same CTE.

The pressure sensor includes a sensor circuit to measure the deflectionof the inner portion of the membrane 210 due to a difference in pressureon opposite faces of the membrane 210. The sensor circuit may includeone or more of a capacitive, piezo-electric, piezo-resistive, straingauge, optical, and/or other circuit which measures the deflection ofthe inner portion of the membrane 210. For example, first and secondsensor elements 244A and 244B are positioned on the inner portion of themembrane 210 to measure the deflection thereof. The pressure sensor mayinclude electronics 246 in the housing 242. The electronics 246 mayinclude a controller which receives a pressure signal from the sensor orsensors and/or a battery. The pressure sensor may generate a relativepressure signal, referring to a pressure signal showing changes in thepressure measured, rather than an absolute measured pressure value.

In some embodiments, the pressure sensor of FIG. 2 is an implantablemedical device incorporating a pressure sensor, and the electronics 246additionally or alternatively include circuitry for the implantablemedical device. For example, in one embodiment, the housing 242 is arelated art implantable pulse generator housing with an opening in theside and the membrane 210 is integrally bonded to seal the opening. Theelectronics 246 include implantable pulse generator circuitry. Acontroller receives the pressure signal from the sensor circuit andcontrols the timing or characteristics of stimulation applied by theimplantable pulse generator circuitry.

In one embodiment, instead of being a separate element bonded to thehousing 242, the membrane 210 is a thinner portion of the housing 242and the tensioning ring 220 is bonded to the thinner portion of thehousing 242, applying a tensile force to the housing to reduce oreliminate defects such as defects introduced in fabrication of thehousing or creating the thinner portion of the housing 242.

FIG. 3A is a plate-tensioned membrane according to embodiments of thepresent disclosure. FIG. 3B is a cross section of the plate-tensionedmembrane of FIG. 3A. A bonding ring 320 bonds a tensioning plate 330 toa membrane 310. The bonding ring 320 has an outer (e.g. circumferential)region which contacts the membrane surrounding an inner region whichdoes not contact the membrane 310. The tensioning plate 330 is parallelto the membrane 310, with a gap 334 between the membrane 310 and thetensioning plate 330 in the inner region of the bonding ring 320. Insome embodiments, a vent hole 332 is included in the tensioning plate330. The membrane 310 may deflect into the gap 334 when under pressure.

The tensioning plate 330 may apply the tensile force to the membrane 310via the bonding ring 320. The tensioning plate 330 may be made of ametal, for example molybdenum, a metal alloy, for example Kovar orInvar, and/or another material, for example fused silica, silicon,glass, or a ceramic. In some embodiments, the tensioning plate 330 has alower CTE than the membrane 310 and the tensioning plate 330, thebonding ring 320, and the membrane 310 are heated to a temperature abovethe anticipated operating temperature range for the pressure sensor whenthey are bonded together. The membrane 310 will contract more than thetensioning plate 330 based on its lower CTE, and the bonding ring 320will accordingly apply a tensile force to the membrane 310 in theoperating temperature range due to being bonded between the two.Alternatively, the membrane 310 may be heated at the time of bonding,resulting in expansion, but the tensioning plate 330 may not be heatedor may be heated to a lesser degree.

FIG. 4 is an embodiment of a pressure sensor utilizing theplate-tensioned membrane of FIGS. 3A and 3B. The membrane 410, tensionedby the tensioning plate 430 via the bonding ring 420, is coupled to ahousing 442. The housing 442 is bonded to the outer portion of themembrane 410. Electronics 446 and first and second sensors 444A and 444Bmay function as described above in reference to the electronics 246 andfirst and second sensors 244A and 244B of FIG. 2 . In one embodiment, anelectrode is coupled to the membrane 410 (or the membrane 410 isutilized as an electrode), tensioning plate 430 is coupled to a counterelectrode (or utilized as a counter electrode), and the electrode (e.g.,410) and counter electrode (e.g., 430) are utilized as a capacitivepressure sensor. The bonding ring 420 may be an electrical insulator,preventing electrical contact between the electrode and the counterelectrode.

FIG. 5 is an embodiment of a pressure sensor according to embodiments ofthe present disclosure. The pressure sensor includes a membrane 510 anda tensioning plate 530 which may be the membrane 410 and the tensioningplate 430 referred to in FIG. 4 . The membrane 510 and the tensioningplate 530 are bonded together by a bonding ring which is made of anadhesive 522 filled with spacing elements 524. The spacing elements 524may have a uniform thickness to provide a uniform distance between themembrane 510 (when not deflected due to pressure) and the tensioningplate 530. In some embodiments, the spacing elements 524 are spheres ofa uniform diameter. The spacing elements 524 are interspersed throughoutthe bonding ring, immersed in the adhesive 522. The adhesive 522 may bean epoxy, and/or may be electrically insulating. The adhesive 522 holdsthe spacing elements 524 in place and bonds the tensioning plate 530 tothe membrane 510, transferring the tensile force. In embodiments whichutilize the membrane 510 as an electrode and the tensioning plate 530 asa counter electrode, both the adhesive 522 and the spacing elements 524may be electrical insulators. In some embodiments, the spacing elements524 are glass or include glass.

FIG. 6A is an exploded view of a ring-tensioned membrane for acapacitive sensor according to embodiments of the present disclosure.FIG. 6B is a cross section view of the ring-tensioned membrane of FIG.6A.

In the ring-tensioned membrane of FIGS. 6A and 6B, a tensioning ring 620again applies a tensile force to a membrane 610. This may beaccomplished as described above. The tensioning ring 620 includes aretaining element 622. The retaining element 622 biases an isolator 676against a counter electrode 630, which in turn biases a spacer 672against the membrane 610. The membrane 610 includes an electrode (or isutilized as an electrode). In some embodiments, a dielectric 674 may beincluded between the membrane 610 and the counter electrode 630 toincrease the dynamic range of the pressure sensor, for example in themanner discussed below in reference to FIGS. 8-10 .

In some embodiments, the retaining element 622 may be a ridge on theinner edge of the tensioning ring 620, as shown in FIGS. 6A and 6B. Inanother embodiment, the retaining element 622 is a portion of thetensioning ring 620 set back from the membrane 610 which does not havethe open inner area, and which therefore encloses the isolator 676, thecounter electrode 630, and the spacer 672 between the tensioning ring620 and the membrane 610.

The isolator 676 and/or the spacer 672 may be electrical insulators. Theisolator 676 prevents the counter electrode from making electricalcontact with the tensioning ring 620. This arrangement may allow boththe tensioning ring 620 and the membrane 610 to be made of conductivematerials such as metals and allow the retaining element 622 of thetensioning ring 620 to bias the counter electrode 630 against themembrane 610 without shorting the membrane 610 and the counter electrode630. It may also facilitate easy coupling of the electrode of themembrane 610 and the counter electrode 630 to a sensorcircuit—connection may be made with the tensioning ring 620 instead ofthe electrode of the membrane 610, in close proximity to the counterelectrode 630.

The spacer 672 is positioned between the membrane 610 and the counterelectrode 630. It provides a uniform distance between the two at theperiphery, but includes an empty (or thinner) inner area. The membrane610 is configured to deflect into the inner area of the spacer 672 whenunder pressure. The tensioning ring 620 applies the tensile force to themembrane 610, so the spacer 672 need not do so. The spacer 672 may notneed to be a ring enclosing the inner area of the membrane 610 whichwill deflect under pressure, and may take additional/alternative forms.For example, the spacer 672 may be a plurality of spacers positionedperiodically at or near the circumferential periphery of the counterelectrode 630.

In some embodiments, the isolator and the spacer are a single piece. Forexample, FIG. 7A is an exploded view and FIG. 7B is a cross section viewof the ring-tensioned membrane for a capacitive sensor shown in FIGS. 6Aand 6B where a spacer 770 with isolator protrusions 776 acts as both theisolator and the spacer. When the spacer 770 is positioned between themembrane 610 and the counter electrode 630, the isolator protrusions 776wrap around the outside edges of the counter electrode 630, preventingit from coming into contact with the tensioning ring 620. The dielectric674 may also be combined into the single piece with the spacer 770 andthe isolator protrusions 776.

FIG. 8A is a capacitor for a capacitive pressure sensor having anincreased dynamic range according to embodiments of the presentdisclosure (see, e.g., FIG. 10 ). FIG. 8B is a first subassembly of thecapacitor of FIG. 8A. FIG. 8C is a second subassembly of the capacitorof FIG. 8A. FIG. 8D is a cross section view of the capacitor of FIG. 8A.

In some embodiments, the membrane 810 is coupled to a tensioning ring820 and the tensioning ring 820 applies a tensile force to the innerportion of the membrane 810, as described above.

An electrode of the capacitor is included in the membrane 810. In someembodiments, the membrane 810 is metal or another conductive materialand the membrane 810 is the electrode. In other embodiments, themembrane 810 is coated or sputtered with the conductive material. Afirst wire 884 is coupled to the electrode and to a sensor circuitconfigured to measure the capacitance of the capacitor to generate apressure signal.

A counter electrode 830 is positioned parallel to the membrane 810. Asecond wire 882 is coupled to the counter electrode 830 and to thesensor circuit to generate the pressure signal by measuring thecapacitance between the electrode of the membrane 810 and the counterelectrode 830. In some embodiments, a plurality of spacers 870 arepositioned between the membrane 810 and the counter electrode 830. In analternative embodiment, the plurality of spacers 870 are replaced withor used in conjunction with a single spacer with a central opening, forexample, a ring-shaped spacer. In one embodiment, spacers 870 arecoupled to the membrane 810 as shown in FIG. 8B. In other embodiments,the spacers 870 may be coupled to the counter electrode 830 or maysimply be biased between the membrane 810 and the counter electrode 830.The thickness of the spacers 870 may define the distance between thecounter electrode 830 and the membrane 810 when the membrane is notdeflected due to a pressure differential. The spacers 870 extend aroundthe periphery of the portion of the membrane 810 which deflects underpressure, leaving a gap between the membrane 810 and the counterelectrode 830 for the membrane 810 to deflect into.

A dielectric 874 is positioned in the gap between the counter electrode830 and the membrane 810. The dielectric 874 is a solid. It may have alow relative dielectric constant. For example, the dielectric 874 may beTeflon, a cyclic olefin polymer (COP), and/or a thin sheet of glass. Itsthickness does not span the distance between the counter electrode 830and the membrane 810, so the membrane 810 can still deflect into the gapdue to pressure. The dielectric 874 may be coupled to the counterelectrode 830. In some embodiments, the dielectric 874 and the spacer orspacers 870 may be combined as one or more pieces of contiguouselectrically insulating material.

In some embodiments, the dielectric 874 is coated or plated directlyonto the counter electrode 830. In some embodiments, the dielectric 874is an oxide layer on metal forming the counter electrode 830 or themembrane 810.

The pressure sensor has an operating pressure range which is the rangeof pressures the pressure sensor is expected to experience duringoperation. The operating pressure range of the pressure sensor whichutilizes the capacitor may include two ranges. In a first range, themembrane 810 deflects into the gap without coming into contact with thedielectric 874. In a second range, the membrane 810 deflects into thegap and comes into contact with the dielectric 874 (the membrane bottomsout). The dielectric 874 may be positioned at the point where themagnitude of the deflection of the membrane 810 is greatest. Increasinglevels of pressure on the membrane 810 will not cause the membrane 810to deflect any deeper into the gap. Instead, increased pressure causesmore of the inner surface area of the membrane 810 to press against thesurface of the dielectric 874.

The sensor circuit may measure the capacitance in this second range inthe course of normal, expected operation. Because the change incapacitance is caused by the deflection expanding outward in themembrane 810, rather than the membrane 810 deflecting further toward thecounter electrode 830, the capacitor does not need as much space betweenthe membrane 810 and the counter electrode 830 and may have a smallerprofile. The distance between the membrane 810 and the dielectric 874may be configured such that the pressure sensor would have lowersensitivity in the second range if it were allowed to deflect furtherinto the gap without contacting the dielectric 874.

In one embodiment, the dielectric 874 is positioned between the membrane810 and the counter electrode 830. A first region of the inner surfacearea of the membrane 810 is in contact with the dielectric 874, while asecond region of the inner surface area of the membrane 810 is not incontact with the dielectric 874. Depending on the pressure differentialbetween the pressure on the inner face of the membrane 810 and the outerface of the membrane 810, the size of the first region may increase ordecrease. The capacitance between the membrane 810 and the counterelectrode 830 changes based on the size of the first region, so thepressure sensor may generate a pressure signal based on the capacitanceof the size of the first region. As a result, the pressure sensor mayhave an improved dynamic range.

In some embodiments, the pressure sensor may be configured to have atleast some portion of the membrane 810 in contact with the dielectric874 during the entire operating pressure range of the pressure sensor.In some embodiments, the pressure inside the pressure sensor may be setat a level to place the pressure differential on the membrane 810 at adesired level in the operating pressure range of the pressure sensor.For example, the pressure sensor may be sealed in an environment with areduced ambient pressure so that the pressure differential on themembrane 810 will cause a larger deflection when the external pressureis in the operating pressure range.

FIG. 9 is an embodiment of a capacitive pressure sensor utilizing thecapacitor of FIGS. 8A and 8B. An outer portion 932 of the membrane 810is bonded to the housing 942. The electronics 946 may be coupled to theelectrode and the counter electrode 830 to measure the capacitancebetween the two, monitor changes in the capacitance due to deflection ofthe membrane 810, and generate a pressure signal based on thecapacitance and/or the changes in capacitance.

Sensor Performance Example

An experiment was performed to measure the performance of a pressuresensor according to embodiments of the present disclosure. A capacitivepressure sensor having a dielectric between the membrane and the counterelectrode was tested over a pressure range from 560 torr to 1000 torr todetermine its dynamic range. The membrane was titanium 6-4 with athickness of 0.17 mm and a diameter of 45 mm. The counter electrode was0.5 mm thick with a 30 mm diameter. A tensioning ring tensioning themembrane had an inner diameter of 34 mm and an outer diameter of 45 mmwith a thickness of 3 mm. The spacer between the membrane and thecounter electrode was 110 micrometers thick, and a 25 micrometer thickTeflon film dielectric was inserted between the membrane and the counterelectrode. FIG. 10 shows the results of the experiment, including boththe capacitance 1010 of the capacitor and the sensitivity 1020 of thesensor at a given pressure. Sensitivity, in this context, refers to theability of the sensor to detect changes in pressure, not an absolutepressure value. Accordingly, sensitivity as used here is the slope ofcapacitance over pressure or the change in capacitance over the changein pressure. From 560 torr to approximately 750 torr, the membrane didnot contact the dielectric. At approximately 750 torr, the membranecontacted the dielectric. At that point, the slope of the capacitance1010 decreases noticeably. At the same point, the slope of thesensitivity 1020 increases noticeably (the sensitivity 1020 decreases ata lower rate).

It will be understood that, although the terms “first,” “second,”“third,” etc., may be used herein to describe various elements,components, regions, layers and/or sections, these elements, components,regions, layers and/or sections should not be limited by these terms.These terms are used to distinguish one element, component, region,layer or section from another element, component, region, layer orsection. Thus, a first element, component, region, layer or sectiondescribed below could be termed a second element, component, region,layer or section, without departing from the spirit and scope of thepresent invention.

It will be understood that when an element or layer is referred to asbeing “on,” “connected to,” or “coupled to” another element or layer, itcan be directly on, connected to, or coupled to the other element orlayer, or one or more intervening elements or layers may be present. Inaddition, it will also be understood that when an element or layer isreferred to as being “between” two elements or layers, it can be theonly element or layer between the two elements or layers, or one or moreintervening elements or layers may also be present.

The terminology used herein is for the purpose of describing particularembodiments and is not intended to be limiting of the present invention.As used herein, the singular forms “a” and “an” are intended to includethe plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises,”“comprising,” “includes,” and “including,” when used in thisspecification, specify the presence of the stated features, integers,steps, operations, elements, and/or components, but do not preclude thepresence or addition of one or more other features, integers, steps,operations, elements, components, and/or groups thereof. As used herein,the term “and/or” includes any and all combinations of one or more ofthe associated listed items. Expressions such as “at least one of,” whenpreceding a list of elements, modify the entire list of elements and donot modify the individual elements of the list.

As used herein, the term “substantially,” “about,” and similar terms areused as terms of approximation and not as terms of degree, and areintended to account for the inherent variations in measured orcalculated values that would be recognized by those of ordinary skill inthe art. Further, the use of “may” when describing embodiments of thepresent invention refers to “one or more embodiments of the presentinvention.” As used herein, the terms “use,” “using,” and “used” may beconsidered synonymous with the terms “utilize,” “utilizing,” and“utilized,” respectively. Also, the term “exemplary” is intended torefer to an example or illustration.

The electronic or electric devices and/or any other relevant devices orcomponents according to embodiments of the present invention describedherein may be implemented utilizing any suitable hardware, firmware(e.g. an application-specific integrated circuit), software, or acombination of software, firmware, and hardware. For example, thevarious components of these devices may be formed on one integratedcircuit (IC) chip or on separate IC chips. Further, the variouscomponents of these devices may be implemented on a flexible printedcircuit film, a tape carrier package (TCP), a printed circuit board(PCB), or formed on one substrate. Further, the various components ofthese devices may be a process or thread, running on one or moreprocessors, in one or more computing devices, executing computer programinstructions and interacting with other system components for performingthe various functionalities described herein. The computer programinstructions are stored in a memory which may be implemented in acomputing device using a standard memory device, such as, for example, arandom access memory (RAM). The computer program instructions may alsobe stored in other non-transitory computer readable media such as, forexample, a CD-ROM, flash drive, or the like. Also, a person of skill inthe art should recognize that the functionality of various computingdevices may be combined or integrated into a single computing device, orthe functionality of a particular computing device may be distributedacross one or more other computing devices without departing from thespirit and scope of the exemplary embodiments of the present invention.

While this invention has been described in detail with particularreferences to illustrative embodiments thereof, the embodimentsdescribed herein are not intended to be exhaustive or to limit the scopeof the invention to the exact forms disclosed. Persons skilled in theart and technology to which this invention pertains will appreciate thatalterations and changes in the described structures and methods ofassembly and operation can be practiced without meaningfully departingfrom the principles, spirit, and scope of this invention, as set forthin the following claims and equivalents thereof.

What is claimed is:
 1. A pressure sensor comprising: a housing having an opening; a membrane coupled to the housing at the opening, the membrane comprising a non-tensioned region bonded to the housing; and a tensioning ring coupled to the membrane to apply a tensile force to the membrane, wherein the non-tensioned region is an area of the membrane outside the tensioning ring; and wherein the membrane and the housing to which the membrane is coupled define a hermetically sealed cavity inside the housing.
 2. The pressure sensor of claim 1, wherein: the membrane has a first coefficient of thermal expansion, the tensioning ring has a second coefficient of thermal expansion lower than the first coefficient of thermal expansion, the membrane and the tensioning ring are to be bonded together in response to being heated above an operating temperature range, and the tensioning ring is to apply the tensile force to the membrane at the operating temperature range.
 3. The pressure sensor of claim 1, wherein the membrane further comprises a tensioned region, the tensioned region being an area of the membrane inside the tensioning ring.
 4. The pressure sensor of claim 1, further comprising a sensor circuit in the housing to generate a pressure signal based on a deflection of the membrane.
 5. The pressure sensor of claim 1, wherein the membrane is a sheet of metal.
 6. The pressure sensor of claim 1, wherein the membrane comprises titanium, stainless steel, or an alloy.
 7. A pressure sensor comprising: a housing having an opening; a membrane coupled to the housing at the opening, the membrane comprising a non-tensioned region bonded to the housing; a tensioning ring coupled to the membrane to apply a tensile force to the membrane, a counter electrode, a spacer, an isolator, and a sensor circuit in the housing to generate a pressure signal based on a deflection of the membrane; wherein the non-tensioned region is an area of the membrane outside the tensioning ring; and wherein: the membrane further comprises an electrode, the counter electrode is positioned parallel to the membrane, the spacer is positioned between the counter electrode and the membrane to provide a gap between the counter electrode and the membrane, the tensioning ring comprises a retaining portion to hold the counter electrode against the spacer, the isolator is to isolate the counter electrode from the tensioning ring, and the sensor circuit is to evaluate a capacitance between the electrode and the counter electrode.
 8. The pressure sensor of claim 7, wherein the isolator and the spacer are connected as a single piece.
 9. The pressure sensor of claim 8, wherein the isolator further comprises a dielectric between the counter electrode and the membrane, the spacer having a first thickness between the counter electrode and the membrane, and the dielectric having a second thickness less than the first thickness.
 10. A method of fabricating a pressure sensor, the method comprising: heating a membrane having a first coefficient of thermal expansion and a tensioning ring having a second coefficient of thermal expansion lower than the first coefficient of thermal expansion to a temperature outside an operating temperature range of the pressure sensor; coupling the tensioning ring to the membrane at the temperature outside the operating temperature range of the pressure sensor while the membrane experiences greater expansion than the tensioning ring so that the tensioning ring applies a tensile force to the membrane when the membrane is at about the same temperature as the tensioning ring; and coupling the membrane and the tensioning ring to an opening in a sensor housing comprising a sensor circuit while the membrane and the sensor housing are at about the same temperature, wherein the membrane comprises a non-tensioned region in an area of the membrane outside the tensioning ring and coupling the membrane and the tensioning ring to the opening of the sensor housing comprises bonding the non-tensioned region to the sensor housing, and wherein the membrane and the sensor housing to which the membrane is coupled define a hermetically sealed cavity inside the sensor housing.
 11. A pressure sensor fabricated according to the method of claim
 10. 